交换两个变量的不同实现方式

#include <stdio.h>

#define SWAP1(a,b) \
{                      int temp = a;      a = b;             b = temp;      }

#define SWAP2(a,b) \
{                      a = a + b;         b = a - b;         a = a - b;     }

#define SWAP3(a,b) \
{                      a = a ^ b;         b = a ^ b;         a = a ^ b;     }

int main()
{
    int a = 1;
    int b = 2;
    
    SWAP1(a,b); //需要一个临时变量
    SWAP2(a,b); //效率低，而且存在溢出的可能
    SWAP3(a,b);
    
    return 0;
}